I enjoy the flow of the writing. Just how O'Shea assembles so many facts I don't know. He provides a "you are there" feeling for the many battles. I am surprised so many details of those battles have survived a millennium. One learns to at least appreciate from this book the value in having adequate supplies of water during a battle. O'Shea apparently visited many of the locations he covers in this book including the battlefields to the extent the exact sites are known nowadays.
That "convivencia", an unusual level of cooperation between Muslims, Christians, and Jews was possible in places during much of the period O'Shea covers, is one good reminder of the value of studying history. One might not suspect given current relationships among these groups that such intellectual and cultural sharing was possible.
On the other hand, the barbarism during the warfare including the Crusades is a reminder of the violence associated with different cultures and religions. The description of Crusader's slaughter of so many defenseless man, women and children in the 1099 ransack of Jerusalem is shocking albeit briefly described. I'm reminded of the destruction of an entire Cather city by Crusaders that O'Shea describes in his earlier work "The Perfect Heresy".
Would O'Shea hope to earn enough from this book to sufficiently reward his major efforts? He must love what he is doing. Hopefully readers will support him in writing histories for a long time.